Automatic wheel cylinder adjustment device for brakes



April' 11,1939. J. A. BAKER 2,154,082

AUTOMATIC WHEEL CYLINDER ADJUSTMENT DEVICE FOR BRAKES Filed Nov. 5, 1957i i k Summer Patented Apr. 11, 1.939

' UNITED STATES AUTOMATIC WHEE MENT DEVICE FOR John a. Baker, Dayton,Ohio, assignor-to General Motors Corporation, Detroit, Mich, acorporation of Delaware Application November 5, 193,7, SerialNo. 172,898

This invention relates to brakes and particularly to brakes for use onvehicle wheels.

More specifically the invention is concerned with a provision forautomatic adjustment of 5 the shoes to accommodate for the wear of thefriction lining material.

An object of the invention is to' provide an improved mechanism of theabove kind wherein the parts have 'a limited free movement under normalcondition of shoe and drum clearance and wherein they may beautomatically adjusted parts displaced from the position they occupy inFigure 3.

Figure 5 is a section on line 5-5 of Figure 3.

Figure 6 is a perspective of one of the parts so used in the secondembodiment of the invention. Referring to the drawing, the numeral 1represents a brake drum, such a drum as is usually carried by androtates with the wheel of a vehicle. The fixed cover or'backing plate ismarked 8.

35 The shoes are designated by numerals 9 and ii. To each shoe issecured friction lining ii. The

I illustratedbrake is one wherein the shoes are spread into contact withthe drum by hydraulic.

applying means including a wheel cylinder i5. 40 The wheel cylinder issecured to the cover 8 in any convenient way. Within the cylinder arepistons I1 with sealing members i9, the pistons being intended to bemoved away from each other by some suitabl'ehydraullc medium, forced be-45 tween them through an opening '21 .by conventional means such as amaster cylinder and conduit system, not shown. As is customary a spring.

23 is placed. between the piston seals to maintain them in contact withthe pistons. A normally 5 closed opening 25 is provided to permit escapeof air. g

Each piston is provided with a steel insert 21 to engage the ends offorks 29 extending from a stem ii, the stem and the forks constituting a5 push rod. One endof the stem II is slotted as position of the latter.

(Cl. 188- -'I9.5).

shown at 33 to engage the web 35 of the shoe. From Figure 1 it will beseen that there is a steep vertical slope- 31 at the other end of thestem adjacentand between the forks 29. A protesting closure 39 of anysuitable kind may be Near each end of the cylinder i5 is a boss 4| andthrough this boss a plunger 43 is mounted for vertical reciprocation.Within the cylinder the plunger 43 has a head 45 notched on its sidefacing the end of the cylinder. The notch includes anupper shorthorizontal wall marked 41, a lower relatively long horizontal wall 49and a connecting sloping surface 5|. A spring 53 between the inner wallof the cylinder and the head it pushes the plunger downwardly. Numeral55 is applied to a wedge having opposite faces corresponding to faces 31and BI, the wedge" being located between the furcations 29 and its facesengaging the faces 31 and ii. The upper and lower f aces" of the wedgeare horizontal and parallel aridgthe vertical extent of the wedgebetween its horizontal faces is somewhat less than the vertical distancebetween surfaces 41 and 49. This difference is marked a on the gdrawing. A shoe retracting spring 51 is attached at its ends to the twoshoes.

The above described arrangement difiers from the conventional by theintroduction of the modifi ed push rod 3| and the associated plunger andwedge device. This device in no way modifies the operation of the wheelcylinder in applying the brakes provided the lining thickness remainsunchanged. The difference a referred to above may be made substantiallythe same as or somewhat greater than the normal desired clearance be--tween the drum and the shoe in the released.

Figure 1 represents the parts in the position they occupy when thebrakes are released, the clearance a being at the top of the wedge. Theretracting spring 51 is stronger than the plunger spring 53. As thefluid under 1 pressure enters the space between' the pistons theyseparate and their movement of separation functions through the pushrod. to overcome spring 51 and to take up/the clearance between theshoes and the drum. As the push rod recip-' rocates and as the tensionof spring 5! is overcome, spring 53 pushes the plunger 43 downwardly,wedge 55 moving horizontally and a space, having a as its maximum.developing between the lower wall 49 and the lower face of the wedge.If, however, the lining It has become worn by previous brakeapplications so that a shoe clear-.

ance exists greater than the predetermined clearhydraulic medium isreleased and the spring 51 restores the parts to the brake releaseposition,

the wedge 55 moves horizontally only and in doing so it pushes plunger,43 upwardly until the clearance or is again present at 41. Thisconstitutes the new release position. There is therefore a new positionof shoe release determined by a new position of the wedge on slope 31, aposition wherein the shoe and drum clearance is again reduced to thedesired extent.

In Figures 3 to 6 inclusive, there is shown another embodiment of theinvention. .In this second form the drum is marked 6|. One of the shoesis shown at 63, the shoe having a lining 64 subject to wear as before.The wheel cylinder is designated as at 61. In this form of the inventionthe cylinder has radially enlarged ends 69 forming shoulders II. Thepiston 13, its packing 15, the opening for hydraulic medium TI and theinner spring 19 for holding the packing against the piston need only bementioned to be under- V stood. The push rod 9|- engagesthe shoe as be-Aligned diametrically opposite apertured bosses 89 and 9I are providedwhich bosses extend from' the enlarged ends 69. Boss 9| is closed by acap 93 and boss 89 by an elongated cap 95. A plunger 91 has its endportions 99 and IIH of cylindrical outline and 'of 'lessdiameter thanthe diameter of the apertures of the bosses of the cylinder within whichthey are located. A spring I03 in abutment with cup 95 engages the topof the end portion 99. Between the end portions 99 and llll is aconnecting stem of rectangular outline marked I05, this stem having a?wedge surface I01 corresponding to the sloping surface I09 of the pushrod between its bifurcated ends. A suitable spring device in the form ofan annular rubber ring I II in the embodiment shown engages the shoulderII and, by means of a metallic clip II3 U-shape in section engages theplunger; ends at diametrically opposite points. This spring III tends toposition the plunger toward the outer region I I5 of the apertures inthe bosses vby reference to Figure 4. If the normal lining clearanceprevails, this action will occur with no vertical reciprocation of theplunger. If, however, the lining is worn so that the shoe clearance isexcessive the, push rodcontinues to advance to such an extent that thespring III reaches its fully expanded condition and is unable to moveplunger 9] further. Under these circumstances spring I93 pushes plunger91 downwardly, the surface I91 sliding alongthe surface I09 until thebrake is fully applied. When the brake is released, the plunger 91retains this new downward position inasmuch as the angle of surface I99is such that there is no effective component acting vertically, capableof over coming spring I03. There is thus provided a new retractedposition for the operating means with the plunger again in contact atII! with substantially the same shoe clearance as before.

I claim:

1 1. In a brake, a drum, a shoe, yielding shoe retracting means,applying means, a push rod with a sloping surface, said push rod beingbetween and in contact with said shoe and said applying means, wedgemeans having asloping surface in contact with the said sloping surfaceof said push rod, a spring operable to move said wedge means along saidsurface to effect a changed release position for-said shoe, and stopmeans to limit the movement of the wedge means in the direction ofmovement of the push rod.

2. The invention defined by claim 1, the end of the push rod engagingthe applying means being forked and said sloping surface being betweensaid forks.

3. The invention defined by claim 1, together with a mechanism toprovide a limited joint movement of said push rod and wedge means in thedirection of the shoe applying movement of th push rod prior to themovement of the wedge means by the spring.

4. The invention defined by claim 1, together with a second springoperable to produce a lim- "ited joint movement of said push rod andwedge means'in the direction of the shoe applying movement of the pushrod. prior to the movement of the wedge means by the first mentionedspring.

5. The invention: defined by claim 1, together with a plunger adapted tobe moved by said spring, said plunger and wedge means having cooperatingsloping surfaces, their angular di' rection being such that a componentof the force of said yielding means may overcome said spring, said. stopmeans being carried by said plunger 6. In a brake, a movable shoe,yieldable retracting means for said shoe, movable applying means,,motiontransmitting means between said applying means and said shoe, a plunger,a

spring to move said plunger across the-path of movement of saidtransmitting means, mechanism cooperating with said plunger andtransmitting mains to predetermine automatically the retracting positionof said shoe under the infiuence of said yielding means. i I I 7. Theinvention defined by claim 6, said yielding means operable to overcomesaid spring means in restoring said shoe to brake released position. 4

8: The invention defined by claim 6, said transmitting means having itsend adjacent said applying means formed with parallel walls and having asloping surface between said-walls and said mechanism having an angularface engaging said sloping surface.

.9. The inventiondefined by claim 6, said mechanism including apartformed integrally ,with

saidplunger and other spring means to move said plunger toalimitedextent jointly with and in the directionof the movement of said transmiting means.

- 1 ma brake,,a drum, a shoe to engage the drum, a reciprocable shoeapplying means, motion transmitting means between said applying meansand shoe, a plunger'reciprocable across the path of movement ofv saidmotion transmitting means, said plunger and transmitting means havingcontacting surfaces defining a plane angularly related to the paths ofmovement of both said plunger and said motion transmitting means andadapted to effect changes in the released position of the shoes,yielding shoe retracting means, first spring means to reciprocate saidplunger and second spring means adapted to move said plunger to alimited extent in the direction of movement of said motion transmittingmeans.

11. The invention defined by claim 10, the yielding shoe retractingmeans being operable to overcome said second spring, said contactingsurface being such that the yielding means may not overcome the firstspring means.

12. In a brake, a drum, a shoe to engagethe drum, shoe applying means,motion transmitting means between said applying means and shoe. a

plunger reciprocable across the path of movement of said motiontransmitting means, a wedge between said plunger and the motiontransmitting means and having angular surfaces in contact with both,said plunger having a head shaped to engage and limit the movements ofsaid wedge relative to and in a direction parallel to the axis of theplunger, spring means to reciprocate said plunger and yielding meansoperable to retract said shoe and reciprocate the motion transmittingmeans, the angularity of the surface contact between the wedge and theplunger being such that the yielding means reclprocates the plungeragainst its spring means, the extent of movement being limited by theengagement between the wedge and the plunger head.

, JOHN A. BAKER.

